Bill Grundmann's
PS99 Vortex Ring Generator



Contents


Description
Parts List
Construction
Operation
Field Testing
Observations About The Smoke Rings
More Observations
Micro VRG
Pocket VRG
Other Vortex Ring Generators
Vortex Ring Links

a close-up of two smoke rings


Description

The PS99 Vortex Ring Generator (VRG) stands 5'8" tall and is 38" deep. The VRG emits smoke rings approximately 3 feet in diameter. Although devices like this are sometimes called a vortex cannon, this is really less like a cannon and more like a big box with a hole in it. It is designed to be easily assembled and disassembled, to be transported in a vehicle such as a Volvo wagon; it needs no more than 5'8" by 3' of floor space. It requires a fog/smoke generator and is manually operated. Construction takes about a week (5 weeknights plus a full weekend). Basic woodworking tools are needed, including a circular saw and scroll saw.

The vortex generator is operated manually by pushing in the large membrane on the back of the unit. The smoke ring emerges from the front of the ring generator. If the VRG is operated outdoors (which is recommended), the air must be calm. The slightest breeze will prevent the rings from forming or explode them instantly.


Parts List


Construction

Four of the plywood sheets are cut to form the front and back parts as well as four of the side pieces. Each side piece should have its 37" edges cut with a 22-1/2 degree bevel. Note that two sheets are cut with the 36" hole; these will be assembled to form the front of the VRG. The other two sheets are cut with the 59" hole; these will be the back of the VRG.

The remaining two plywood sheets are cut to make the other four side pieces. Each side piece should have its 37" edge cut with a 22-1/2 degree bevel.

The pine trim is cut into sixteen 2' lengths. Attach them to the front and back using the tee-nuts, washers and screws. Use two screws per edge. For the edge that bridges across the two front and two back edges, use four screws. Leave a 1/2" gap between the trim and the edge to allow room for the sides.

Lay the assembled front piece on the floor and temporarily attach three of the eight side pieces using one wallboard screw per edge. Attach the assembled back on top of the three side pieces using one wallboard screw per edge.

Now fit the remaining side pieces one at a time. Some hand-fitting of the beveled edges will probably be necessary.

Once all the pieces are fitted, add more wallboard screws, totaling five per edge.

Remove the back by removing the screws from the tee-nuts. Lay the shower curtain or rubber sheet across the opening and re-attach the back to hold it in place. Punch holes for the screws to pass through the curtain or sheet.

Cut the two sheets of foam-core to form octagons. Punch a 1/4" hole in the center of each. (Note: We discovered that when using a rubber sheet there is no need to use the foam-core octagons, just using your hand is sufficient.)

Cut a 4" hole in a side piece for the dryer hose. (Note: We found that using a portable fog generator to fill the unit through the main hole in the front worked quite well. If you use it this way, the dryer hose and hole can be skipped.)

Stand the unit up. Locate the center of the shower curtain, and punch a 1/4" hole there. (Note: If using a rubber sheet, punching a hole in it is unnecessary, and you can skip the next section that describes the assembly of the octagon.)

Assemble the 4" screw, one nut, one washer, and one foam-core octagon. Leave about half of the screw extending on the outside so that it can be grasped during operation of the VRG. Place this on the outside of the VRG, carefully threading the screw through the hole in the shower curtain.

On the inside of the unit, assemble the other foam-core octagon, one washer, and one nut onto the screw protruding through the hole. It may be necessary to reinforce the shower curtain at the central hole by using a vinyl patch kit.

We found that using a rubber sheet works very well. The entire octagon thing can be skipped. You might be able to find this sold as a roofing supply. It is similar to inner tube rubber.

Attach the fog machine to the VRG using the dryer hose. (No need to do this if you use a portable fog machine.)



the VRG in action


Operation

Allow the fog machine to fill the VRG with smoke. A shutter made of poster board may be needed to contain the smoke. Remove the shutter carefully (to avoid creating turbulence) just prior to launching a smoke ring. (Note: we found there was no need to do this if you use a portable fog machine.)

Gently pull the foam-core outwards using the protruding screw. After a few seconds, push the foam-core inwards and hold it there. This launches the smoke ring. Experiment with the timing, amount of force, and distance moved: these control the size, speed, and duration of the smoke rings. (Note: we found that when using a rubber sheet, simply forcefully pushing in it at the center works fine. A good punching motion works too.)



Field Testing

The VRG was tested in an outdoor setting. The generated rings were about three feet in diameter. The VRG is extremely sensitive to breezes; even a very light breeze interferes with ring formation and propagation.

For maximum visibility and minimum wind problems, I recommend scheduling demonstrations near sunset. The indirect light makes the rings highly visible. And it seems that the breezes of the day tend to die down at that time of day.

If the air is calm enough, you can try generating smoke rings during daylight hours. The rings are readily visible even in direct sunlight.

Lighting the rings after dark is a difficult problem. A little experimentation seemed to show that side lighting might be the best approach. Perhaps a follow spot would be effective also.


Observations About The Smoke Rings

One thing about a three foot smoke ring is that you can easily observe lots of cool detail.


a very smokey ring being chased by a second ring

The first thing to notice is the amount of force carried by the ring. It seemed like much of the work done by the operator in forming the ring is carried very efficiently by the ring. As it drifts along at about 5 to 10 feet per second, it seems that little of the energy is lost.

Most of the rings we made were still going strong when they crashed into the trees. The leaves rustled quite a lot at the point of impact, making it very easy to tell where the ring went. This helped the operator fine tune his aiming. He got pretty good at it. We could stand where the ring would go. When you get hit by a three foot smoke ring, you know it! It's like a strong wind gust right in your face.


this ring has lost almost all of its smoke as it heads into the trees

As far as we could tell, these rings would have continued much further than the 60 feet or so that they had room to move through before hitting the trees. I'm not sure how they would dissipate: would they suddenly explode, or just "rope out"? A few we saw did that: it looked very much like a tornado roping out. A few times a light breeze came up that almost stalled the ring in place. Those definitely demonstrated the roping out effect.

I wonder if a vortex ring can be called a soliton? They seem to share the similar characteristic of behaving like a non-dissipating object.

The structure of the smoke rings is surprising. The actual inner core of the ring is about 2 inches in diameter. The perfectly formed rings maintained their shape throughout their flight, looking almost solid.

The inner core is clear air! Looking at the ring from the front you can tell it looks a little lighter around the core. But seen edge-on, it is obviously clear air in there. You can see two clear circles at the top and bottom parts of the core.


the core of this ring is clear

The smoke is carried somewhat turbulently around the core. Some of the smoke streams away behind the ring as it moves. We even saw a few rings lose all their smoke and continue on invisibly (indicated by rustling leaves).

Why is the core clear? Two possibilities I can suggest are: the core air was drawn in from the region in front of the VRG, or the speed of rotation centrifuges out the smoke. But the rings are not always clear; notice here that it seems to be filled with smoke.


the core of this ring is not clear

More experimenting is called for!


More Observations

On Labor Day I demo'ed the VRG at my parents' house. With the gracious help of some friends, we transported it there a few days beforehand.

The weather forecast was marginal, but it went great. Between the rain and gusts of wind there was actually about 1/2 hour of dry calm before dinner. I shot a few rings past the back windows of the house and drew a few people outside. The rings were backlit by the sun and were highly visible. Then the most incredible rainbow I've seen in quite a while appeared... Everyone was outside gawking at that - it was a double rainbow. There was no competing with that spectacle, so I took a break, then we went inside for dinner.

Again after dinner we had a period of no rain and very light breezes. Finally everyone got to see lots of rings. Some blew up on launch, some flew a little way, but a few drifted very far. One stalled in a breeze and simply got thinner and thinner until it broke up.

I gave all the kids plenty of tries at making their own rings. They all succeeded. Even my littlest niece hit the VRG (very gently) and a perfectly round, slow motion ring drifted out. It was amazing! It happened twice.


Micro VRG

An empty gallon size plastic water bottle makes a great micro VRG! Hold the bottle against your chest to stabilize it. Use one hand to hold the bottle by its handle, leaving the other hand free. Aim the open end at a target (for instance a piece of paper on a table). Now, using your free hand, tap the side of the bottle. With a little practice, an invisible vortex ring will shoot out and hit the target. (If you're a smoker, fill it with smoke first.) Cats do not like being shot at in this manner.


Pocket VRG

Here's an idea for a much more portable pocket sized Vortex Ring Generator from Jeff Hoover (jeffhoover @ bigfoot.com).

  1. Open a hard pack (box) of cigarettes with the cellophane pull-tab and leave most of the cellophane on the box.
  2. Slide the cellophane down the box 2/3 to 3/4 of the way and set the box on a flat surface.
  3. Holding a lit cigarette perpendicular to the flat surface, carefully plunge the ember through the center of the largest surface of the cellophane.
  4. Take a drag on the cigarette and carefully blow the smoke into the hole in the cellophane.
  5. Tap the surface of the cellophane and a ring should launch straight up out of the hole in the cellophane.


Smoke Ring Nebula

Naa... it's not really a smoke ring... but it sure looks cool.


from www.astronomy.org


Other Vortex Ring Generators

Zero Toys, Inc. sells these sweet hand-held vortex ring generators, Zero Launcher and Zero Blaster

Here's a device that makes air rings under water The Bubble Rings Ring Machine.

A version of this VRG is being built by the Society of Physics Students at the University of Missouri - Kansas City: Giant Vortex Ring Generator

University of Virginia Physics Show's vortex generator.

Physics Van, a traveling science show in Illinois, includes a vortex ring generator.

University of Melbourne Lecture Demonstration has plans for a smoke ring generator.


Vortex Ring Generator Links

Why Does Smoke "Ring"? Check out this animation!

Excerpt from "Ring Bubbles of Dolphins" Dolphins intentionally produce underwater vortex rings Mystery of the Silver Rings Toys that dolphins make for themselves

Vortex Ring / Wall Interactions aiming rings at a flat wall

University of Michigan Vortex Ring Transit Experiment NASA Get Away Special Payload G-093 Experiment Description NASA - STS-88 Payload Bay UMSEDS Experiment Studies Propagation of a Vortex Ring Through a Liquid-Gas Interface in Microgravity Aboard Space Shuttle Endeavour

UCLA - USA - 1952 College of Engineering, Report of the Dean Vortex Rings for use in tree spraying as well as for picking nuts.


THIS INFORMATION IS FREE FOR YOUR PERSONAL USE.

Bill Grundmann 1999


in memoriam